A standard chuck assembly has an actuator cylinder centered on and rotatable about an axis but substantially nondis-placeable relative to the axis and a chuck housing spaced axially from the cylinder. A tubular connecting shaft extending along the axis is connected fixedly between the cylinder and the chuck housing so that the cylinder, connecting shaft, and chuck housing rotate jointly about the axis but do not move along the axis. A chuck piston axially displaceable in the chuck housing has an inner end turned axially toward the actuator cylinder and an actuator piston is axially displaceable in the cylinder. The chuck piston and actuator piston are axially interconnected by a shaft assembly comprising an actuator shaft fixed to the actuator piston and having an outer end and a chuck shaft having an inner end connected to the actuator-shaft outer end and an outer end connected to the chuck-piston inner end. The chuck has radially displaceable jaws operated by its piston so that a workpiece can be gripped between these jaws and rotated about the axis for machining.
The actuator piston defines in the actuator housing a pair of compartments and the actuator housing has a rearwardly extending connection sleeve formed with a pair of passages each having one end opening into a respective one of the compartments and an opposite end opening radially outwardly at locations offset axially from each other and from the piston and actuator housing. A distributor body is mounted on this connection sleeve and has fittings connected to two fluid supply lines that can be alternately pressurized and depressurized. This body is rotatable about the main axis on the connection sleeve and can even move axially limitedly with this connection sleeve.
Fluid can be fed under pressure alternately to the fittings to pressurize and depressurize the respective compartments and thereby axially displace the piston in the cylinder since the cylinder is connected to the chuck body and the piston to the chuck-actuating piston or member for actuation of the actual chuck jaws. Double check valves built right into the piston inhibit flow out of either of the compartments unless one of the passages is pressurized.
The region where the connector body rides on the rapidly rotating connection sleeve of the actuator housing can get fairly hot, especially as seals are provided flanking the locations where radially inwardly or outwardly open grooves on one of the parts confront radially outwardly or inwardly open ports on the other part for fluid transfer between the parts. In order to cool this region it has been suggested simply to provided fan-like vanes on the cylinder housing, which rotates at high speed with the chuck body, to force air over this region.
The problem with this system is that the air-circulating structure generate considerable hum. The machine-shop environment is noisy enough under the best of circumstances, so this additional source of sound is considered highly undesirable.